JPH01208834A - Etching method - Google Patents

Abstract

PURPOSE:To improve the accuracy of etching for fine working by using the mixed gas of an isotropic etching gas being represented by SF6 and having large reactivity and an anisotropic etching gas containing heavy ions easy to be dissociated to a symmetrical shape. CONSTITUTION:A mixed gas mainly comprising at least one kind of a gas selected from a group composed of SF6, CF4, NF3, XeF2 and F2 as an isotropic etching gas and at least one kind of a gas (where X represents at least one kind selected from a group consisting of Cl, Br, I and H) selected from a group made up of (CXF2)2, (CX2F)2 and (CX3)2 is employed, and plasma etching is conducted. Accordingly, since etching can be performed by extremely low high frequency power, a resist can be used as an etching mask, and a vertical etching hole 3 can be formed when an Si substrate 1 is etched, employing the resist 2 as the mask.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an etching method, and particularly to a dry etching method suitable for forming fine grooves with high precision.

[Conventional technology] For processing fine patterns such as semiconductor integrated circuits.

A dry etching method using reactive gas plasma is used. Typical etching gases include isotropic etching gas such as Si or GaAs, F2. SFg, NF3-.

XeF2. As a CF4y anisotropic etching gas, CF
3CO, CF2CO2, CFCQ3. cQ2゜CCn4
．． CBrF3. ClF3 and the like are known. Regarding these etching gases, for example, JP-A-51'-1
No. 30173, JP-A-52-9648, JP-A-57-
13137, etc.

In isotropic etching, since etching is mainly performed using electrically neutral particles, it is difficult to perform highly accurate processing according to mask dimensions. Therefore, when microfabrication or the etching shape is desired to be vertical, anisotropic etching is performed using ions accelerated from plasma toward the surface of the material to be etched.The most common method is one-reactive dry etching. Therefore, etching gases that cause etching by electrically neutral particles have been selected, and those that allow etching to proceed solely through the action of ions have been selected.

[Problems to be Solved by the Invention] In the above-mentioned conventional technology, since etching is performed by ions accelerated by a negative direct current bias, there are problems such as damage to the substrate due to ion bombardment and collisions between the accelerated ions and gas molecules. There were problems such as side etching caused by changing direction and colliding with Si, and etching conditions differing between lots in order to knock out oxygen adsorbed on the furnace wall.

Among the above problems, as a method to reduce ion damage, SF8, which is an isotropic etching gas, and anisotropic etching gas, such as CQ2, CeO2, CC12FB,
A mixed gas with 5iCQ4 etc. is also used. but,
Even in these cases, the problem of side etching was not solved, and the etching shape was susceptible to change depending on the mixed gas ratio and etching conditions.

An object of the present invention is to provide an etching method using a mixed gas that solves this problem.

[Means for Solving the Problems] The above purpose was achieved by using SF6. which is an isotropic etching gas. C.F.
4. NF3. at least one type of gas selected from the group consisting of XeF2 and F2, and anisotropic etching gases (CXF2)2゜(CX2F)2 and (CX3)
This can be achieved by using a mixed gas whose main component is at least one type of gas selected from the group consisting of 2. However, the above X is at least one selected from the group consisting of 8Q, Br, I and H.

Among these gases, SF is more preferable as the isotropic etching gas, and (CBrF2)2 is more preferable as the anisotropic etching gas, from the viewpoint of ease of gas availability.

[Function] Plasma in dry etching contains various ions and neutral particles, and among these, substances mainly composed of C and S adhere to the substrate surface as reaction residues and inhibit etching. On the other hand, since various ions are accelerated and collide with the substrate surface, they not only etch the substrate, but also serve to remove deposits. Etching with a mixed gas of an isotropic etching gas and an anisotropic etching gas makes good use of the above two functions to perform etching with a vertical etching shape as shown in FIG.

Specifically, when the radio frequency power is very low, the ions are not accelerated enough and the deposits, which are reaction residues, are removed, but the etching of the substrate by the ions is very small; The etched portions are easily etched by highly reactive neutral particles of F (mainly contained in the isotropic etching gas). In this way, etching occurs more and more in areas where ions are bombarded, so the etching shape depends on the ion directionality.

In other words, if most of the ions are incident perpendicularly to the substrate, the etched shape will be vertical, but if they collide with gas molecules etc. on the way and are scattered, the shape will not be vertical, and as shown in Figures 2 and 3. It will look like shown.

For example, when the gas pressure is 10 Pa and the ion sheath width is 1 mm, it is said that about 60% of the ions collide with gas molecules during acceleration, are scattered, and change direction. Therefore, it is necessary to reduce the influence of scattering as much as possible, and methods for doing so include: - lowering the gas pressure to sufficiently increase the mean free path; and - lowering the high-frequency power to reduce the ion energy at the time of collision. It is important to select ions whose scattering angle is as small as possible.

The mixed gas according to the present invention described above satisfies the above conditions. That is, the anisotropic etching gas (for example, (CBrFz)z) in the above mixed gas becomes two CBrF2'' ions or neutral particles when the C-0 bond is broken. It is a heavy ion, and the above ■
It satisfies the requirements of The same applies to gases according to the present invention other than (CBrFz)2.

[Example] A plasma etching device having an anode-coupled parallel plate electrode was used as the etching device, and a mixed gas of SF6 and C2Br2F4 was used as the gas.
Si was etched using the resist as a mask. The electrode of the etching device has a diameter of 20 cm and the high frequency power supply frequency is 13
．． It is 56MHz.

First, the object to be etched is placed on the electrode, the etching chamber is evacuated to below 10-'Pa, and the SFB is heated to 32SCCM.
, C2Br2F4 was introduced at 8SCCM, and the indoor pressure was increased to 10Pa.
Etching was performed for 20 minutes at a high frequency power of 0.03 W/d while maintaining the temperature. The etching speed at this time was 1100n.
/min, and etching was performed to a depth of 2 μm.

FIG. 1 is a cross-sectional view of the etching process, and almost vertical etching was achieved in this way. The width of the etching hole is 0.5μ
It is m. Although the mixing ratio of SB6 and C2Br2F4 is 4:1 in the above example, it is preferably in the range of 3:1 to 20:1 under normal vacuum and high frequency power.

Etching mask 2 is made of Si○2 or Si3N in addition to resist.
Similar results were obtained when using 4. The etching selection ratio (etching speed ratio with Si) is approximately 15.
It was 100 or more for SiO□ and Si3N4. However, when etching was performed under conditions where the high frequency power exceeded 0.30 W/d, the etching selectivity became smaller at higher power. From this point of view, the high frequency power is 0.3
W/d or less is preferable.

A good cross-sectional shape can also be obtained by further mixing F2 or He with the mixed gas of SF6 and C2Br2F4, which is preferable.

Since these have a small mass, CBr with a molecular weight of about 130
This is thought to be because the effect of collision with F2+ ions is small.

Other etching gases include CF 41 NF 3 e X e F 2 which is a monoisotropic etching gas.
It is also an anisotropic etching gas such as #F2 (
CCQ F2) 2-(cc Q2F) 2. (c
c Q3) 2. (CI F2) 2y(CBr2
F)2 etc. are also SF6. It showed similar characteristics to C2Br2F4. However, with a gas containing CQ, there was a tendency for side etching to occur depending on the etching conditions. This is because heavy ions are further decomposed into lighter ions. When a mixed gas of SF6 and CCU4 was used for comparison, when the mixture ratio of CCQ4 was 15% or more, or even when the mixture ratio was 5%, the pressure was 0, I Tor
A good etched shape could only be obtained in a narrow range, with side etching occurring at r or more.

NF3 instead of SF6. CF4. XeF2 and F2°
A good etched shape was also obtained when using 5Fllll, but the range of conditions was slightly narrower than when using 5Fllll. This was thought to be due to the difference in the way reaction residues adhered to the substrate.

From the above results, plasma etching can be performed using a mixed gas of a highly reactive isotropic etching gas such as SF and an anisotropic etching gas containing heavy ions that are easily dissociated into a symmetrical pattern. It has become clear that fine and deep holes can be etched with high precision. In this case, it is more preferable to perform plasma etching with relatively low radio frequency power.

It should be noted that the above gases may be used in combination of three or more types, and the above X is not only one type in the same molecule, but also B.
It goes without saying that it may contain multiple types of elements such as r and CQ.

[Effects of the Invention] According to the present invention, since etching can be performed with extremely low high frequency power, the resist can be used as it is as an etching mask, and the thickness of the resist may be small.

In addition, there is no need to worry about harmful effects caused by sputtering of oxygen adsorbed on the walls, allowing ultra-fine processing to be performed with good reproducibility.6Furthermore, ion bombardment of the substrate is eliminated, resulting in improved device characteristics.

When ions decomposed by plasma are heavy, the dependence on etching conditions is reduced compared to when lighter ions are used.

[Brief explanation of the drawing]

FIG. 1 is an etched cross-sectional view obtained by the present invention, and FIGS. 2 and 3 are etched cross-sectional views when affected by ion scattering. 1...Si substrate, 2...resist, 3...etching hole.

Claims (1)

[Claims] 1. At least one type of gas selected from the group consisting of SF_6, CF_4, NF_3, XeF_2, and F_2, and the group consisting of (CXF_2)_2, (CX_2F)_2, and (CX_3)_2. An etching method characterized in that plasma etching is performed using a mixed gas of at least one type of gas selected from the following (where X is at least one type of gas selected from the group consisting of Cl, Br, I, and H). 2. Claim 1, wherein the mixed gas is a mixed gas of SF_6 and (CBrF_2)_2.
Etching method described in section. 3. The etching method according to claim 1 or 2, wherein the etching is performed at a high frequency power of 0.3 W/cm^2 or less. 4. The etching method according to claim 1 or 2, wherein He or H_2 is added to the mixed gas.